Coaxial cable with spiral spacer



June 10, 1952 H. D. ISENBERG 2,600,111

COAXIAL CABLE WITH SPIRAL. SPACER Original Filed Feb. 8, 1946 JNVENTOR.HANS. D. ISENBERG WWW Patented June 10, 1952 CQAXIAL CABLE WITH SPIRALSPACER D. Isenberg, Wilmette, 111..

Original application February 8, 1946, Serial No. 646,464. Divided andthis application Novem= her 12, 1947, Serial No. 785,271

(Cle 174 253) 4 Claims.

The present invention relates to air or gas insulated or coaxial cable.This application is a division of applicants copending application Ser.No. 646,464, filed February 8, 1946,, now Patent 2,434,073.

Coaxial cable of the air or gas insulated type used commercially in wideband high frequency circuits is conventionally comprised of twocoaxially arranged conductors which are held apart by insulating discsprovided at spaced points along the two conductors to support the innerconductor centrally within the outer conductor and thus provide adielectric air or gas space therebetween.

This construction is not only costly, but requires 1 that the cable beformed in relatively short lengths or sections which must be joined inorder to obtain a cable of any considerable length.

It is an object of the present invention, therefore, to provide animproved air insulated or coaxial cable that may be continuously formedto e any desired length.

It is another object of the invention to provide an improved coaxialcable structure which may be economically constructed on a continuousand fully automatic basis and yet is of rugged construction, such thatit may be roughly handled and distorted in use without loss of itselectrical properties.

It is still another object of the invention to provide an insulatingfilament of improved construction uniquely adapted for use incontinuously forming the improved coaxial cable herein disclosed.

The invention, both as to its organization and method of operation,together with further objects and advantages thereof, will best beunderstood by reference to the following specification taken inconnection with the accompanying drawing, in which:

Fig. 1 is a side view partially in section, illustrating a segment ofthe finished cable characterized by the features of the presentinvention; and

Fig. 2 is a sectional view taken along the lines 2-4 in Fig. 1.

Referring now to the drawings, the present improved air insulated orcoaxial cable is there illustrated as comprising a continuousfilamentary element II of plastic insulating material wound into helicalconvolutions I3 disposed along the length of the inner conductor I2 ofth cable, and so constructed that certain thereof, 1. e., theconvolutions 13a are radially spaced from the conductor to support anouter sheath 21, and others thereof, 1. e., the convolutions I312 engagethe conductor I2 at spaced points along the length thereof to supportthe radially spaced convolutions 1311 from the conductor.

More specifically considered, the filament l I is made of a heatsettable or heat annealable plastic which has the property of beingsettable in a fixed configuration, either when heated to a predeterminedtemperature, or when heated to a semi-plastic state and then cooled.Specifically this filament may be formed of a phenolic resin, a methylmethacrylate resin, 2. vinyl chloride acetate resin, a polystyreneresin, a polyvinyl chloride resin or any material having similarproperties. This filament is of novel construction. As best shown inFig. 1, the filament is of generally Z-shaped cross-section and isprovided with rabbets on opposite sides and at the opposite marginsthereof so that it may be formed into helical convolutlons with eachconvolution interlocking with the adjacent convolution to form arabbeted joint. The surface Ila of the filament, which is adapted tocontact the conductor 12, isshown as being arcuate, but may be anynon-planar surface that will provide minimum contact, i. e.

l a line contact between the conductor I2 and the filament II. Thisminimum contact is an important feature of the improved filament,because tests have established that at ultra-high frequencies dielectriclosses decrease with a decrease in the amount of contact between aconductor and a dielectric. Preferably, the outer surface Nb of thefilament is planar in order that the interlocking convolutions of thefilament may form a member having a substantially continuous outersurface. This is especially desirable if the outer sheath 2! is anon-conductor. If, however, the sheath 21 is a conductor such that thestructure forms a coaxial cable, and if dielectric losses are to bereduced to a minimum, the surface lib may also be a non-planar surface.As will be understood, the plastic filament ll possesses elasticity sothat the cable may be bent through a fairly short radius, if necessary.

The improved method and apparatus used in continuously making thepresent improved cable are fully disclosed and claimed in applicant'scopending application Ser. No. 646,464, now Patent 2,434,073. Briefly,the method embraces the steps of continuously moving the inner conductorl2 longitudinally, winding the continuous filamentary element H ofinsulating material about the conductor 12 to form th helicalconvolutions which surround the conductor ll, actuating a windingmandrel to so change the diameter of winding that the convolutions [3aare radially 3 spaced from the conductor 12 and convolutions I3b engagethe conductor 12 at spaced points therealong, and then forcing theadjacent convolutions toward each other to increase the overlap betweenthe complementary rabhets of the filament l i and thus form a continuousunbroken sheath around the conductor 12. During the last-described step,heat is applied to the convolutions [3 to eirect setting thereof wit-hfull overlap therebetween.

From a further consideration of the drawing, it will be noted that theresulting insulating supporting structure comprises spaced groups ofconvolutions [3a of equal diameter which are radially spaced from theinner conductor 12 and are alternated with convolutions l3?) whichembrace the conductor l2 and serve to support the radially spacedconvolutions I30. from this conductor. It will also be understood thatsince the thermo-plastic or thermo-setting filamentary element H isheated to its setting or annealing temperature incident to the formationof the convolutions, a permanent set is imparted to the convolutions 13which enhances the tendency of these convolutions to reassume the formedpositions thereof when distortion pressures imposed thereon arerelieved.

Concurrently with formations of the helical convolutions l3 in themanner just described, the outer sheath 2! of the insulating orconducting material is progressively wound around the convolutions l3 tocomplete the cable structure. This material is in strip form and may beself-adhering so that the overlapped thereof are bonded to preventseparation after the serves to enhance the rigidity of the completedcable structure.

While there has been described what is at present considered to be apreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein which a are within the truespirit and scope of the invention as defined in the appended claims.

I claim:

1. An insulated cable comprising an inner conductor and a continuousfilament of either thermosetting or thermoplastic material helicallywound around said conductor to itself form a continuous flexible sheath,the convclutions of said sheath being interlocked with rabbet joints,

said sheath having certain convolutions found so as to providesubstantially a one turn spiral of reduced diameter directly contactingsaid conductor and radially spacing it from the remainder of saidconvolutions.

2. An insulated cable comprising an inner conductor, and a continuousfilament of either thermosetting or thermoplastic material wound inhelical convolutions around conductor, certain of said convolutionsbeing radially spaced from said conductor and others of saidccnvolutions of reduced diameter being wound to provide substantiallyone turn spirals directly contacting and supporting said conductor, thespaced convoluticns having interlocking edges, whereby they formacontinuous flexible sheath around said conductor.

3. An insulated cable comprising a continuous electrical conductor, atubular outer covering, and insulating means supporting said conductorcentrally within said covering and spacing the same therefrom, saidinsulating means compris ing a filament having a non-plane surface on atleast one side thereof and complementary rabbets at opposite margins andon opposite sides of said filament, said filament being formed intosuccessive groups of helical convolutions joined by interlocking of saidrabbets and arranged in contact with said outer covering and having asingle complete convolution intermediate each of said groups directlysupporting said conductor and helically disposed thereon with thenonplane surface of said filament contacting said conductor and with theopposite ends of the intermediate convolutions each merging in gradualcurvature with the end of an adjacent corresponding helical convolutionof a group.

4. A coaxial cable, comprising a continuous electricalinner conductor,an outer conductor surrounding the same and insulating means sup portingsaid conductors in coaxial relationship. said insulating meanscomprising a continuous plastic filament having complementary ra sets atopposite margins and on opposite sides thereof, and said filament beingwound in helical convolutions around said inner conductor therebyforming an unbroken flexible sheath which contacts said outer conductor,with substantial portions of certain convolutions surrounding anddirectly contacting said inner conductor spacing it from the remainingconvclutions.

HANS D. ISENBERG.

REFERENCES CITED The rcllowing references are of record in the- .de ofthis patent:

UNITED STATES PATENTS and

